Scientists have for the first time looked at HIV infection within the actual tissue of an infected organism.

Researchers at the California Institute of Technology (Caltech) utilised high-resolution electron microscopy to achieve what may be the most detailed characterisation yet of HIV infection in the gut.

"Looking at a real infection within real tissue is a big advance," said Mark Ladinsky, lead author of the paper.

"With something like HIV, it's usually very difficult and dangerous to do because the virus is an infectious agent. We used an animal model implanted with human tissue so we can study the actual virus under, essentially, its normal circumstances," said Ladinsky.

Ladinsky worked with Pamela Bjorkman, Max Delbruck Professor of Biology at Caltech, to take three-dimensional images of normal cells along with HIV-infected tissues from the gut of a mouse model engineered to have a human immune system.

The team used a technique called electron tomography, in which a tissue sample is embedded in plastic and placed under a high-powered microscope.

Then the sample is tilted incrementally through a course of 120 degrees, and pictures are taken of it at one-degree intervals.

All of the images are then very carefully aligned with one another and, through a process called back projection, turned into a 3-D reconstruction that allows different places within the volume to be viewed one pixel at a time.

"Most prior electron microscopy studies of HIV have focused on the virus itself or on infection of laboratory-grown cell cultures," said Bjorkman, who is also an investigator with the Howard Hughes Medical Institute.

"Ours is the first major electron microscopy study to look at HIV interacting with other cells in the actual gut tissue of an infected animal model," said Bjorkman.

By procuring such detailed images, researchers were able to confirm several observations of HIV made in prior, in vitro studies, including the structure and behaviour of the virus as it buds off of infected cells and moves into the surrounding tissue and structural details of HIV budding from cells within an infected tissue.